As a process for the production of inorganic or metal thin films, MOCVD has been widely applied, and as MOCVD materials, metal alkoxides, β-diketone complexes, etc. have been developed. Of these, 2,2,6,6-tetramethyl-3,5-heptanedione and 2,6-dimethyl-3,5-heptanedione are known to form volatile complexes together with relatively many kinds of metals, but these compounds have not become so widespread industrially because they are expensive.
A process using Claisen condensation is well known as a process for preparing the 2,2,6,6-tetramethyl-3,5-heptanedione. For example, in J. Am. Chem. Soc., 66, 1220 (1944), ethyl pivalate is reacted with pinacolone (3,3-dimethyl-2-butanone, tert-butyl methyl ketone) using a sodium amide catalyst to synthesize 2,2,6,6-tetramethyl-3,5-heptanedione in a yield of 28%. In this literature, acylation reaction of methyl ketone with an ester using sodium ethoxide is also described, and it is reported that the reactivity is inferior when a higher ester is used.
In J. Org. Chem., 27, 1036 (1962), methyl pivalate is reacted with pinacolone using a sodium hydride catalyst to synthesize 2,2,6,6-tetramethyl-3,5-heptanedione in a yield of 60 to 70%.
Other examples of the process for preparing 2,6-dimethyl-3,5-heptanedione using Claisen condensation reaction have also been reported (Bull. Inst. Chem. Res. Kyoto Univ., vol. 46, No. 6,256 (1968) and Mat. Res. Soc. Symp. Proc., vol. 495, 63 (1998)). In any of these processes, however, sodium hydride or sodium amide that is difficult to handle similarly to the metallic sodium is used as a catalyst, and there resides a problem of safety. Moreover, safety countermeasures thereto are necessary, and hence, it is difficult to use these processes industrially.
In addition to the above processes, a synthesis process using Grignard reaction of malonyl chloride with t-BuMgCl (t-Bu is a tert-butyl group) and a synthesis process using a reaction of malonyl chloride with t-BuCu(Li)SPh have been reported. In these processes, however, an extremely low temperature of about −70° C. is necessary, and handling is very difficult. Thus, there are problems in the industrial practice.
As described above, any industrially advantageous process wherein 2,6-dimethyl-3,5-heptanedione can be prepared by simple and easy operations at a low cost has been unknown so far, and further improvement has been desired.